"Then sawed his hand off with an old hacksaw, cutting through flesh, bones, nerves, and major arteries. He'd pass out and go into shock and bleed out. But I know people have done this and survived with IMMEDIATE modern medical care... so I can suspend disbelief temporarily. Then, though, he fights through and kills several zombies and cauterizes his would with a searing iron." Far fetched ill agree, but im very confident that there have been live people who have done very close to exactly this.